Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $242.45   10.273%   $267.3569   $267.36   $267.35   $267.40  
  Purchase #2 $239.81   13.188%   $271.4361   $271.44   $271.45   $271.40  
  Purchase #3 $156.55   8.816%   $170.3514   $170.35   $170.35   $170.40  
  Purchase #4 $15.30   13.498%   $17.3652   $17.37   $17.35   $17.40  
  Purchase #5 $124.67   6.392%   $132.6389   $132.64   $132.65   $132.60  
  Purchase #6 $162.60   13.366%   $184.3331   $184.33   $184.35   $184.30  
  Purchase #7 $26.68   11.415%   $29.7255   $29.73   $29.75   $29.70  
  7 purchase totals = $968.06       $1,073.2071   $1,073.22   $1,073.25   $1,073.20